Identifying structural isomers using retention index - Qualitative analysis of mixed xylenes in lacquer paint using msFineAnalysis iQ
Introduction
Typically, qualitative analysis using GC-QMS involves library database (DB) searches using mass spectra obtained by electron ionization (EI) method. However, when qualitative analysis is performed based solely on the similarity to the library spectrum, depending on the compound, multiple significant candidates may be obtained, or the wrong candidate may be selected as the identification result. Therefore, it is effective to use the method in combination with soft ionization (SI) methods such as photoionization (PI) to confirm the molecular ion. In this case, two measurement data, one from the EI method and one from the PI method, are obtained for one sample, making data analysis more complicated, so an integrated qualitative analysis software capable of analyzing the two data quickly and automatically is desirable. To this end, we have developed an integrated qualitative analysis software called "msFineAnalysis iQ" that automatically combines the analysis results of the EI method and the SI method.
However, when the target compound for qualitative analysis contains structural isomers, it may be difficult to distinguish them using only mass spectra. In this case, identification using the retention index (RI) in combination is useful. The retention index is an indicator of the time a compound is retained on a GC column, and each compound has its own unique retention index. Therefore, by comparing the retention index measurement value of an unknown compound with the retention index of a known compound, the compound can be identified.
In this study, a commercially available lacquer paint was measured by pyrolysis GC/MS. Then, integrated qualitative analysis was performed using msFineAnalysis iQ. In this MSTips, we will report an identification example of mixed xylenes (xylol) using retention index.